?????? is a key concept in biology. The Academies are involved in helping those who are interested in science understand evolution theory and how it is permeated throughout all fields of scientific research. This site provides students, teachers and general readers with a variety of educational resources on evolution. It also includes important video clips from NOVA and WGBH produced science programs on DVD. Tree of Life The Tree of Life is an ancient symbol that represents the interconnectedness of all life. It is used in many spiritual traditions and cultures as a symbol of unity and love. It can be used in many practical ways in addition to providing a framework to understand the history of species, and how they respond to changes in environmental conditions. The first attempts to depict the biological world were based on categorizing organisms based on their physical and metabolic characteristics. These methods, based on the sampling of different parts of living organisms or small fragments of their DNA, significantly increased the variety that could be represented in a tree of life2. These trees are mostly populated of eukaryotes, while the diversity of bacterial species is greatly underrepresented3,4. Genetic techniques have greatly broadened our ability to visualize the Tree of Life by circumventing the requirement for direct observation and experimentation. Trees can be constructed using molecular techniques such as the small subunit ribosomal gene. The Tree of Life has been greatly expanded thanks to genome sequencing. However there is still a lot of biodiversity to be discovered. This is particularly true of microorganisms, which are difficult to cultivate and are often only found in a single specimen5. Recent analysis of all genomes produced an unfinished draft of the Tree of Life. This includes a wide range of archaea, bacteria and other organisms that haven't yet been isolated or the diversity of which is not fully understood6. This expanded Tree of Life is particularly useful in assessing the diversity of an area, helping to determine if certain habitats require protection. ??????? can be used in a variety of ways, from identifying the most effective medicines to combating disease to enhancing crop yields. This information is also valuable in conservation efforts. It can aid biologists in identifying areas that are likely to have cryptic species, which may have important metabolic functions, and could be susceptible to changes caused by humans. While conservation funds are important, the best method to protect the biodiversity of the world is to equip more people in developing countries with the necessary knowledge to act locally and promote conservation. Phylogeny A phylogeny (also known as an evolutionary tree) illustrates the relationship between different organisms. Scientists can construct a phylogenetic diagram that illustrates the evolutionary relationships between taxonomic groups using molecular data and morphological differences or similarities. Phylogeny is essential in understanding biodiversity, evolution and genetics. A basic phylogenetic Tree (see Figure PageIndex 10 ) is a method of identifying the relationships between organisms that share similar traits that have evolved from common ancestors. These shared traits could be either analogous or homologous. Homologous characteristics are identical in terms of their evolutionary path. Analogous traits may look similar however they do not have the same ancestry. Scientists arrange similar traits into a grouping known as a Clade. Every organism in a group share a characteristic, like amniotic egg production. They all evolved from an ancestor who had these eggs. A phylogenetic tree is constructed by connecting clades to identify the organisms which are the closest to one another. Scientists utilize DNA or RNA molecular information to construct a phylogenetic graph which is more precise and detailed. This information is more precise and gives evidence of the evolution of an organism. The analysis of molecular data can help researchers identify the number of organisms that have an ancestor common to them and estimate their evolutionary age. The phylogenetic relationships between species can be influenced by several factors, including phenotypic plasticity a kind of behavior that changes in response to unique environmental conditions. This can cause a trait to appear more resembling to one species than another and obscure the phylogenetic signals. This problem can be mitigated by using cladistics. This is a method that incorporates a combination of homologous and analogous traits in the tree. In addition, phylogenetics can help predict the length and speed of speciation. This information can aid conservation biologists in making decisions about which species to safeguard from extinction. Ultimately, it is the preservation of phylogenetic diversity that will lead to a complete and balanced ecosystem. Evolutionary Theory The main idea behind evolution is that organisms change over time as a result of their interactions with their environment. A variety of theories about evolution have been developed by a wide range of scientists, including the Islamic naturalist Nasir al-Din al-Tusi (1201-1274) who envisioned an organism developing slowly according to its requirements as well as the Swedish botanist Carolus Linnaeus (1707-1778) who conceived modern hierarchical taxonomy, and Jean-Baptiste Lamarck (1744-1829) who suggested that the use or non-use of traits cause changes that could be passed on to offspring. In the 1930s and 1940s, theories from various fields, including genetics, natural selection and particulate inheritance -- came together to form the modern evolutionary theory synthesis which explains how evolution occurs through the variations of genes within a population and how those variations change in time as a result of natural selection. This model, which encompasses genetic drift, mutations, gene flow and sexual selection can be mathematically described. Recent discoveries in the field of evolutionary developmental biology have revealed that genetic variation can be introduced into a species through genetic drift, mutation, and reshuffling of genes during sexual reproduction, as well as by migration between populations. These processes, in conjunction with others such as the directional selection process and the erosion of genes (changes in frequency of genotypes over time), can lead towards evolution. Evolution is defined by changes in the genome over time, as well as changes in the phenotype (the expression of genotypes in an individual). Students can better understand the concept of phylogeny through incorporating evolutionary thinking throughout all aspects of biology. A recent study by Grunspan and colleagues, for instance, showed that teaching about the evidence supporting evolution helped students accept the concept of evolution in a college-level biology course. For more information on how to teach evolution look up The Evolutionary Power of Biology in All Areas of Biology or Thinking Evolutionarily A Framework for Infusing Evolution into Life Sciences Education. Evolution in Action Traditionally, scientists have studied evolution through studying fossils, comparing species and observing living organisms. Evolution is not a distant event, but a process that continues today. Bacteria evolve and resist antibiotics, viruses evolve and elude new medications, and animals adapt their behavior in response to a changing planet. The results are often evident. But it wasn't until the late 1980s that biologists understood that natural selection can be seen in action, as well. The key is that various characteristics result in different rates of survival and reproduction (differential fitness) and can be transferred from one generation to the next. In the past, if one allele - the genetic sequence that determines colour - appeared in a population of organisms that interbred, it could be more common than any other allele. In time, this could mean that the number of moths that have black pigmentation in a population may increase. The same is true for many other characteristics--including morphology and behavior--that vary among populations of organisms. It is easier to see evolution when a species, such as bacteria, has a high generation turnover. Since 1988, Richard Lenski, a biologist, has been tracking twelve populations of E.coli that descend from a single strain. Samples of each population have been collected regularly, and more than 500.000 generations of E.coli have been observed to have passed. Lenski's research has demonstrated that mutations can alter the rate at which change occurs and the effectiveness at which a population reproduces. It also shows evolution takes time, a fact that is hard for some to accept. Microevolution is also evident in the fact that mosquito genes for resistance to pesticides are more prevalent in areas where insecticides are used. This is due to the fact that the use of pesticides creates a pressure that favors individuals with resistant genotypes. The rapid pace of evolution taking place has led to a growing awareness of its significance in a world shaped by human activity--including climate changes, pollution and the loss of habitats which prevent many species from adjusting. Understanding evolution will help us make better choices about the future of our planet, as well as the lives of its inhabitants.
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